Divide the ground beef into four equal size pieces, and use your hands to roll each one into a loose ball. Smash the burger down with your palm until it’s about ½ inch thick. Sprinkle both sides generously with salt and pepper.
Heat a thin layer of vegetable oil in a cast iron skillet over medium high heat. Add the burger patties to the pan, as many as you can fit, and cook, undisturbed, 3-4 minutes, or until the bottom side has a nice browned crust.
Flip the burgers and add the cheese. Continue to cook another 3-4 minutes, or until burgers are cooked through, reaching an internal temperature of 160 degrees. Remove the burgers to a plate and allow to rest, covered in foil, for about five minutes.
To serve, layer the bottom buns with the lettuce and tomato, followed by the burger patty, bacon, and mac and cheese. Top with pickled onions and jalapenos, as desired. Serve immediately.